The spectrum of $Li^{2+}$ is similar to that of:

If the potential energy of an electron in a hydrogen atom is $-3.02 \ eV$,then the electron is present in which of the following excited states?

The radii of two of the first four Bohr’s orbits of the hydrogen atom are in the ratio $1 : 4$. The energy difference between them may be

The surface of sodium metal is irradiated with radiation of wavelength $x$ nm. The kinetic energy of ejected electrons is $2.8 \times 10^{-20}$ $J$. The work function of sodium is $2.3$ eV. The value of $x$ is . . . . . . $\times 10^2$ nm.

The ratio of the radius of the $2^{nd}$ orbit of $H$ to the radius of the $3^{rd}$ orbit of $He^{+}$ is ......

The energy of an electron in the first orbit of $He^{+}$ is $-871.6 \times 10^{-20} \ J$. What will be the energy of an electron in the first orbit of hydrogen?